I have a Nokia Lumia 800, a nokia N8, old N73 and an iPhone 4. Out of these 4, sound quality of lumia 800 is the worst, still. Now I use Kilpsch Image S4's. Even with no equalizer preset, Nokia N8, Iphone and even N73 deliever fair amount of bass. Lumia is straight flat. I dont know if they should add an equalizer or an update but Sound quality is letting me down with this otherwise awesome phone.
You are not alone. There is a thread dedicated to Lumia 800 audio quality.